MassQC Help > Metrics > Identifications > Mass Accuracy          
Mass Accuracy

Mass Accuracy is the difference between the mass observed with the mass spectrometer and the known mass of the peptide precursor molecule.

Mass Accuracy closer to zero is indicative of better instrument tuning and stability.

The Mass Accuracy metric is the median of the mass accuracy of all the spectra that have been matched to peptides.

Units:

Parts per million (ppm)

Optimal:

Zero: This metric, unlike most metrics in MassQC, can be either positive or negative.

What the Metric Detects:

The Mass Accuracy metric shows how close the measured mass is to the real mass. If the measurement is made numerous times, the accuracy is the difference between the average value and the real mass. The accuracy is not the same as the precision which is the scatter in repeated measurements.

If the Mass Accuracy is different from zero, it means that the mass spectrometer is consistently reporting the masses as too high or two low.

Related Metrics:

The Precursor m/z reports the median value of the peptide precursors but doesn't say anything about how accurately they are measured. If there are very few Peptides or MS2 Spectra, then the Mass Accuracy metric will not be as good an estimate of the true mass accuracy.

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